Sulphur-35 radiotracer studies of the effect of hydrogen sulphide on a molybdenum disulphide catalyst in the hydrogenation of buta-1,3-diene
Hydrogenation of buta-1,3-diene on a molybdenum disulphide catalyst has been studied in order to determine the change in the pattern of butene product distribution with catalyst treatment (with hydrogen, a buta-1,3-diene + hydrogen mixture, air, hydrogen sulphide or a thiophene + hydrogen mixture). Catalyst treatment with sulphur compounds (H2S or thiophene + H2) resulted in a butene product distribution closer to thermodynamic equilibrium proportions than for a catalyst treated with hydrogen or air. 35S has been used as a tracer in H2S to measure the quantity of H2S necessary to change the catalytic function on fresh and hydrogen-treated catalysts and to observe the extent of sulphur isotopic exchange of gas-phase H2S with MoS2-lattice sulphur and with adsorbed H2S. Evidence is presented for the participation in the hydrogenation reaction of hydrogen present as adsorbed HS groups on the MoS2 surface, and the change of catalytic function with H2S treatment has been interpreted in terms of the change in distribution of these HS groups.